In general, liquid crystal display (LCD) devices can be divided into the following three categories according to use of different sources of lighting: (1) transmissive, (2) reflective, and (3) transreflective. A transmissive LCD device typically has a backlight source for generating light. The light generated by the backlight source passes through the liquid crystal unit and various optical components (such as a polarizer) to illuminate a picture in the LCD device that is viewable by a user. A reflective LCD device has a reflecting surface (formed of aluminum, for example). Light (such as ambient light or light from a front light source) enters the reflective LCD device from the front of the panel, passes through the liquid crystal unit and various optical components, and is reflected by the reflecting surface. The reflected light travels through the liquid crystal unit and the various optical components to illuminate a picture in the LCD device that is viewable by a user.
A transreflective LCD device features characteristics of both transmissive and reflective LCD devices; when ambient light is relatively strong or when weaker light is desired for display, the LCD device can turn off the backlight source and display the picture in a reflective mode by using the ambient light as the light source. However, when the ambient light is relatively weak or when stronger light is desired for display, the transreflective LCD device can turn on the backlight source and display the picture in the transmissive mode.
Conventional transreflective LCD devices either use a transreflective reflector for reflecting the ambient light from outside so that the LCD device can display the picture in a reflective mode, or allow the light generated by the backlight source to pass through a transreflective reflector so that the LCD device can display the picture in a transmissive mode. The transreflective reflector reflects part of the light and allows the rest of the light to pass through.
As shown in the example of FIG. 1, which is a schematic drawing of the basic configuration of a typical transreflective LCD device 1, the transreflective LCD device 1 includes: an upper polarizer 2, a retardation film 4, an upper glass substrate 6, an upper transparent electrode 8, a liquid crystal layer 10, a lower transparent electrode 11, a lower glass substrate 12, a light diffuser 13, and a reflecting polarizer 14. The reflecting polarizer 14 includes a multi-layered dielectric film which reflects light when ambient light 9 is used as the light source, or allows light from a backlight source (not shown) to pass through when the backlight source is used.
A conventional technique used in some LCD devices involves the use of different liquid crystal cell gaps to achieve the effects of transmission and reflection. FIG. 2 shows a conventional transreflective LCD panel with different liquid crystal cell gaps. In the transmissive area, a transparent ITO electrode 17 is used, while in the reflective area, a metal layer 18 that can reflect the light is used as an electrode. A liquid crystal layer 19 has different layer thicknesses at different locations. The liquid crystal cell gap in the reflective area is half (or even less) of the liquid crystal cell gap in the transmissive area. The arrangement depicted in FIG. 2 includes dual gaps. An upper polarizer and lower polarizer 15 and an upper and a lower quarter-wave plate 16 in the display area cooperate to provide the transmissive and reflective effects. However, the manufacture process for forming the dual gap configuration is often complicated and difficult.